Spools for carrying photosensitive or developed photographic film are well known in the art. Spools used for microfilm are generally standardized according to dimensions provided by the American National Standards Institute, Inc. in ANSI PH1. 33-1972. During use of these spools, it is generally necessary to secure one end of the film to the core of the spool. U.S. Pat. No. 3,330,494 describes the general structure of such a spool. In order to secure the film to the core of such a spool, various locking mechanisms have been devised. U.K. Pat. No. 1,343,082 discloses a core having a slot in its surface which leads to a cavity within the core. Film is slid between the flanges and is inserted into the core through the slot to lock it into place. Not only is it somewhat difficult to thread the film into the slot, but also the locking mechanism in the core is not as secure as is desirable.
Locking mechanisms are commercially available for use with spools having a slit on at least one flange from the exterior edge of the flange to the interior of the core which intersects a slot in the core. These locking mechanisms comprise flexible polymeric segments in various forms which can be compressed to fit easily within a section of the core and which then expand to secure the segment within that section. By providing a slot in the segment to lodge the end of the film strip, the film can be directed to pass around the segment before it passes through the slot in the core. The expanded segment will therefore press the film strip against a surface in the core and lock it into place. These locking mechanisms require an existing slit in at least one flange which intersects the slot in the core. These mechanisms are therefore not useful for holding developed film on spools used for photosensitive film which must have flanges that are opaque and continuous.